1. Field of the Invention
The present invention relates to a light source unit and a projector including this light source unit.
2. Description of the Related Art
In these days, data projectors are used in many cases as image projection apparatuses which project screens or video images of personal computers and further images based on image data stored in memory cards on to a screen. These projectors are such that light emitted from a light source is concentrated on a micromirror device called a DMD (Digital Micromirror Device) or a liquid crystal plate for display of a color image on the screen.
In projectors of the type described above, conventionally, projectors using a high-intensity discharge lamp as a light source have been the mainstream of projectors. In recent years, however, there have been made many developments and proposals on light source units which use as a light source, a solid-state light emitting device such as a light emitting diode, a laser diode or an organic DL. For example, the applicant of this patent application has already proposed a light source unit including a light source for emitting light in the wavelength range of blue and a light emitting wheel which has a fluorescent material layer which absorbs light emitted from the light source to convert the light into visible light and which is driven to rotate by a motor and a projector including this light source unit.
In this light source unit, three colors of light, red, green and blue, can be emitted sequentially from the light emitting wheel (a rotary plate), on which a fluorescent material layer as a light emitting member and a diffusion layer are placed to lie adjacent to each other circumferentially, by shining directional blue light on to the light emitting wheel.
Here, the light emitting wheel of the light source unit is normally formed by bonding a fluorescent plate and a diffusion plate to a rotating shaft of the motor, for example. The fluorescent plate includes integrally a member having a fluorescent material layer which emits light in the wavelength range of red and a member having a fluorescent material layer which emits light in the wavelength range of green, and the diffusion plate which is placed adjacent to the fluorescent plate and which diffuses light in the wavelength range of blue from the light source for emission.
In a case where the light emitting wheel is formed in the way described above, the fluorescent plate which is formed of a metal has a fan-like shape having an arc larger than a semicircle and has a circular opening portion into which the rotating shaft of the wheel motor can securely be fitted. Since the wheel motor is installed in this opening portion so as to penetrate therethrough, the light emitting wheel is fixed firmly. In contrast to this, the diffusion plate which is formed of a resin or glass has a fan-like shape having an arc smaller than a semicircle and is secured to the rotating shaft of the wheel motor and the fluorescent plate only through bonding. Consequently, there has been a possibility that the diffusion plate which is bonded to the fluorescent plate comes off due to deterioration with age thereof or external shock or vibration imposed thereon. Because of this, in order to prevent light from the light source from being emitted directly to the outside of the light source unit, there has been a need to have a countermeasure for stopping the operation of the light source by detecting the coming off of the diffusion plate by a controlling means.
In addition, in projectors which utilize a high output light source such as a laser light source, various proposals have been made for adoption on means for preventing light outputted from the light source from being emitted directly to the outside of a light source unit. For example, Japanese Unexamined Patent Application No. 2000-267621 proposes a picture display system including a light source for emitting laser light, a beam converting means such as a lens for converting a beam of laser light from the light source into a thick beam, an image generating means for generating an image by the beam of laser light whose thickness has been so converted, a detection means such as a photosensor for detecting whether or not the beam converting means operates normally, and a laser light limiting means for stopping or attenuating the radiation of laser light based on information from the detection means or a picture display device as a cut-off means which is provided on an optical path for cutting off laser light.
In the picture display system described above, the attenuation or stoppage of radiation of laser light is implemented or the cutting off of laser light is implemented based on the information from the detection means, thereby making it possible to prevent a direct emission of high-output laser light to the outside of the light source unit.
Although various countermeasures like the proposal described above have been adopted, since there is a need to include the detection means such as the photosensor and the control unit such as the laser light limiting means which is activated to operate based on information from the detection means, a problem has been caused that the configuration of the picture display system becomes complex, resulting in an increase in production costs. In addition, in the event that there occurs a situation in which laser light is outputted to the outside by an unforeseen condition, the light source is attenuated or stopped or light from the light source is cut off by the information from the detection means being inputted into the control means. Because of this, there has been caused a problem that a slight time lag is generated in implementing such an attenuating or stopping operation or light cut-off operation.